Methane Direct Injection in an Optical SI Engine - Comparison between Different Combustion Modes
Methane Direct Injection in an Optical SI Engine - Comparison between Different Combustion Modes
复制标题
DOI：
10.4271/2019-01-0083
复制
发表时间：
2019-01
期刊：
影响因子：
--
通讯作者：
M. Melaika;M. Andersson;P. Dahlander
中科院分区：
文献类型：
--
作者：
M. Melaika;M. Andersson;P. Dahlander
© 2019 SAE 国际。版权所有。天然气、沼气和生物甲烷因其有益的物理和化学特性而成为压缩天然气 (CNG) 发动机有吸引力的燃料。本文研究了光学单缸发动机中的三种燃烧模式：均质化学计量、均质稀薄燃烧和分层燃烧，该发动机配备气体直喷系统，喷射压力为 18 bar。通过指示参数、记录燃烧图像和分析燃烧化学发光发射光谱来表征每种模式的燃烧过程。纯甲烷是 CNG（高达 98%）或生物甲烷（> 98%）的主要成分，被用作燃料。化学发光发射光谱分析表明，在所有三种燃烧模式中，OH* 和 CN* 峰都出现在其特征波长处。 OH* 和宽带CO 2* 强度的峰值强烈依赖于气缸中的空气/燃料比条件。在稀空气/燃料混合物中观察到较低的 OH* 和 CO 2* 强度，因为在这些条件下，存在更多的空气，燃烧反应更慢，并且气缸压力更高。 CN* 由火花等离子体形成，并且在使用双线圈点火系统时在特别长的时间内被检测到。使用该点火系统时，OH* 和 CN* 信号的强度相关。燃烧图像分析表明，火焰在化学计量和稀薄燃烧模式下具有皱纹边界，并且在分层模式下尤其扭曲。在均匀燃烧过程中没有观察到黄色烟灰发光。然而，分层燃烧过程中获得的发射光谱和燃烧图像表明，由于气缸内存在富含燃料的区域且混合不充分，因此发生了碳烟形成。维持稳定的燃料喷射、实现适当的空气/燃料混合以及确保贫空气/燃料混合物中稳定的火焰传播的困难增加了循环间的变化。然而，均质稀薄燃烧和分层燃烧模式实现的指示比燃料消耗值明显低于化学计量燃烧。
© 2019 SAE International. All Rights Reserved. Natural gas, biogas, and biomethane are attractive fuels for compressed natural gas (CNG) engines because of their beneficial physical and chemical characteristics. This paper examines three combustion modes - homogeneous stoichiometric, homogeneous lean burn, and stratified combustion - in an optical single cylinder engine with a gas direct injection system operating with an injection pressure of 18 bar. The combustion process in each mode was characterized by indicated parameters, recording combustion images, and analysing combustion chemiluminescence emission spectra. Pure methane, which is the main component of CNG (up to 98%) or biomethane (> 98 %), was used as the fuel. Chemiluminescence emission spectrum analysis showed that OH∗ and CN∗ peaks appeared at their characteristic wavelengths in all three combustion modes. The peak of OH∗ and broadband CO 2 ∗ intensities were strongly dependent on the air/fuel ratio conditions in the cylinder. Lower OH∗ and CO 2 ∗ intensities were observed with lean air/fuel mixtures because under these conditions, more air was present, the combustion reactions were slower, and the cylinder pressure was higher. CN∗ was formed by the spark plasma and was detected over a particularly long period when using a dual coil ignition system. The intensities of the OH∗ and CN∗ signals correlated when using this ignition system. Combustion image analysis showed that the flame had a wrinkled boundary in stoichiometric and lean burn modes and was especially distorted in stratified mode. No yellow soot luminescence was observed during homogeneous combustion. However, the emission spectra and combustion images acquired during stratified combustion showed that soot formation occurred due to the presence of fuel-rich areas with inadequate mixing in the cylinder. The difficulty of maintaining stable fuel injection, achieving proper air/fuel mixing, and ensuring stable flame propagation in lean air/fuel mixtures increased cycle-to-cycle variations. However, the homogeneous lean burn and stratified combustion modes achieved significantly lower indicated specific fuel consumption values than stoichiometric combustion.